The private language problem is essentially the question of whether or not a language as a system of symbols that are means of thinking is, of necessity, a language as a system of symbols that are means of communication. Defining "private language" as language (in the sense of means of thinking) which in principle the speaker alone can understand (so that it cannot serve as a means of communication), our question is roughly equivalent to: "Is a private language possible?" Many philosophers, following Ludwig Wittgenstein, have made the claim (here called the private language thesis, abbreviated PLT) that private languages are impossible. Armed with it, they have argued against solipsism, phenomenalism, the analogical or empirical view of one's knowledge of other minds, and against mind-body dualism. Some of them have gone on to argue for certain versions of philosophical behaviorism as well as for...